Screw clamp with u-shaped clamp part

ABSTRACT

In a screw clamp (2) for connecting electrical conductors (36), the clamp body has a U-shaped sheet-metal component (4) between the arm sections (5, 6) of which is held a nut (9) to accept a clamping screw (11) and in which the end section (12) of the first arm section (5) is bent through 90° towards the second arm section (6), bears upon the latter and has an opening (17) though which the clamping screw (11) can be inserted. To improve the mechanical strength of such a screw clamp (2) while at the same time reducing its structural height, the end section (15) of the second arm section (6) is also bent towards the first arm section (5) and has a screw opening (18), with the two end sections (12, 15) and the nut (9) being in mutual contact. This screw clamp is suitable for particularly high loading owing to lateral extensions (24, 25) of the outer end section (12) which transfix suitable recesses (27) in the inner end section (15) and mutually engage, and owing to a widening of the bridge (23) between the recess (7) and the screw opening (18) in the inner end section (15).

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to a screw clamp for connecting electricalconductors.

European patent 0 023 234 suggests one type of screw terminal forconnecting electrical conductors. That screw terminal is used, forexample, in conjunction with a one-piece molded receptacle as thecontact element for a cable connector. No thread grooves can be madefrom the thin spring steel sheet necessary for those screw terminals,and the required tightening torque cannot be attained with a simple holefor accommodating the terminal screw. Therefore, between two legsections of the screw terminal there is a sufficiently thick nut (crossnut) that is held using side shoulders in recesses of the two legsections. In this way the leg section clearance can be reduced to thediameter of the threaded hole and thus a minimum width of the screwterminal can be achieved, preferably the diameter of the screw headcorresponding at most to this width.

In this screw terminal however, a relatively large leg length isnecessary in order that the leg part between the recesses and the freeupper edge is thick enough to be able to accommodate the clamping forcesproduced by the required tightening torque of the terminal screw. Forthis reason, the terminal height (i.e., the dimension in the directionof the screw axis) is too large for many applications, especially foruse in miniature connectors.

In addition, in the known screw terminal, under high clamping forces,the leg sections can be pressed apart by more than the materialthickness of the sheet metal, therefore the cross nut is withdrawn atleast from one recess, and reliable terminal contact is no longerguaranteed. Frequently, the screw terminal in this process is deformedso that it is unusable.

An advantage of this screw clamp is that it is simple and inexpensive.Another advantage is that the screw clamp has stability in the directionof the screw axis, the terminal height is reduced, and spreading of theterminal arm sections is reliably prevented even under high clampingforces.

This screw clamp structure, which is implemented with a minimumadditional cost compared to previous structures, makes it possible toarrange the inside surface of the end part of the second arm section tobe supported directly on the cross nut so that the range of heightsnecessary to accommodate the clamping forces is reduced to twice thematerial thickness of the sheet metal part. Thus, the clamp dimensionsare reduced not only in width but also in height to an absolute minimumby which the range of application of the screw terminal is greatlyincreased. This screw clamp can, for example, be used in miniatureconnectors with contact carriers in cross section that have varioussmall contact cavities for holding one-piece contacts with the screwterminal connection.

Moreover, by means of the aligned screw openings of the inner and outerend part of the two arm sections, which preferably correspond to theoutside diameter of the threaded shaft of the terminal screw or whichare at least slightly larger, lateral yielding of the arm sections, atleast in the area of the recesses adjacent to the end parts, issuppressed both simply and effectively so that even with very largeclamping forces, the mechanical stability of the screw terminal isreliably guaranteed on a permanent basis.

The design also easily and simply prevents the arm sections fromspringing to the outside before inserting and screwing down the clampscrew. This greatly facilitates assembly. In addition, the extensionsbent into the recesses result in the fact that the two end parts of thearm sections lie next to one another transversely to the screw axis inthe target position and are held together -- in this way, they can beeasily inserted into the recesses of equipment parts, said recessesadapted to the target cross sectional outline, for example, to thecontact cavities of a connector-contact carrier; this likewisecontributes to easy assembly. One such screw terminal is thus especiallywell suited for mechanical mass production of products such asconnectors.

Furthermore, securely holding the end parts together prevents the outerend part from folding upwards at higher tightening torques. Theextensions could fundamentally also be molded onto the inner end partand provide for insertion into recesses of the outer end part. In thisversion, however, the lugs that project over the outer end part wouldagain make the terminal height greater. The arrangement in which thelugs project into the free space between the two arm sections on theirlongitudinal ends conversely has the advantage that the minimum terminalheight is preserved. For many cases, a lug that projects laterally oneach extension is adequate. An especially high retaining force andexactly parallel position of the two parts to one another are achievedwith extremely low additional material cost by lugs (or a double lug)adjacent to both sides to the neck.

At the minimum width of the U-shaped clamp part, the clearance of thearm sections corresponds to the outside diameter of the threaded shaftof the terminal screw. After the cross nut sits against the innersurface of the inner end part of the second arm section with minimumadditional terminal height, on the bending edge of the second armsection between the recess boundary edge facing it and the, for example,circular bushing, there remains only a narrow bending bridge. On thefront free end of the inner end part where the bushing runs tangentiallyto the front edge there is essentially no bridge. The danger, therefore,is great that the screw clamp will not withstand the loads at thesepoints under high tightening torques, and the narrow bridges willrupture. The site on the front free end of the inner end part, moreover,cannot be reliably controlled in production engineering.

To prevent this danger, however, advantageous measure are included.

By forming the opening of the inner end part the bending bridge isgreatly widened by the height of the remaining circular segment thatcorresponds to the difference between the outside radius of the threadedshaft and it core radius. In this way, the acquired widening ismaximized and the remaining circular segment fits as a screw brake andscrew locking device into the screw thread.

Another improvement in the stability of the bending bridge by wideningis included. By means of the arrangement and dimensioning of the jog, itbends equally in area with the inner end part and thus widens thebending bridge by the material thickness of the sheet metal part withoutprojecting out laterally beyond the second arm section so that theminimum width of the U-shaped clamp part is preserved. This bendingbridge widened in such an extremely simple and cost favorable mannerwithstands the mechanical loads that occur under the strongest clampingforces.

By an additional design of the opening of the inner end part the sheetmetal part is suitable, for example, in punching processes withoutadditional costs for series production, because no undefined thinbridges or tips can occur. Sickle-shaped claws, surrounding the screwshaft and formed by slightly shortening the inner end part, arerelatively durable and are also reliably protected against opening underthe action of high clamping forces.

BRIEF DESCRIPTION OF THE DRAWINGS

The design is detailed below in the figures using an embodiment formedas a terminal bushing for a cable connector.

FIG. 1 shows a view of the sheet metal part of the screw clamp.

FIG. 2a shows a front view of the terminal bushing with a terminalscrew.

FIG. 3 shows an overhead view of the cross nut, not installed.

FIG. 4 shows a connection-side front view of the connector-contactcarrier with the terminal bushings inserted.

FIG. 5 shows a partially cutaway side view of the contact carrier withterminal bushings inserted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a view of the sheet metal part of the screw clamp. FIG. 2ashows a front view of the terminal bushing with a terminal screw. FIG.2b shows a lateral view of the terminal bushing with a terminal screw.FIG. 2c shows an overhead view of the terminal bushing without aterminal screw. FIG. 3 shows an overhead view of the cross nut, notinstalled.

Terminal bushing 1 has terminal screw 2 and two fork springs 3 that forma receptacle contact and that are molded in one piece to the terminal.Screw terminal 2 has U-shaped spring steel sheet metal part 4 (shown inFIG. 1 ) that is produced in a punching and bending process, with twoarm sections 5, 6 in each of which there is recess 7, into whichshoulders 8 of cross nut 9, which lie opposite one another, fit withcentral threaded hole 10 to accommodate terminal screw 11 to such anextent that they are flush with the outside wall of arm sections 5, 6.In this way, not only is the cross nut 9 stably retained, but it is alsopossible to adapt the clearance between arm sections 5, 6 to the screwdiameter and thus minimize the terminal width.

One end part 12 of first arm section 5 is bent by 90° around firstbending edge 13 towards second arm section 6. The front edge 14 is flushwith the outside wall of second arm section 6. One end part 15 of secondarm section 6 is likewise bent 90° towards first arm section 5 aroundsecond bending edge 16 and is located between outer end part 12 andcross nut 9. Outer end part 12 lies on inner end part 15 and the latterin turn on cross nut 9 so that the clamp height is low yet has highstability.

Two end parts 12, 15 each bear central openings 17, 18 for terminalscrew 11. Opening 17 of outer end part 12 of first arm section 15 iscircular with the diameter of the circle corresponding to the outsidediameter of threaded shaft 19 of terminal screw 11. Opening 18 of innerend part 15 of second arm section 6 in a central area is likewisecircular with the indicated diameter; in the area facing bending edge16, the circle is shortened by a segment with chord 20 parallel tobending edge 16, which has a distance corresponding to the core radiumof threaded shaft 19 from the center of the circle M. In addition,boundary edge 21 of recess 7 facing bending edge 16 has jog 22 thatcorresponds to the material thickness of sheet metal part 4 so thatbetween recess 7 and opening 18 a relatively wide and stable bridge 23is formed, which also effectively prevents rupture of sheet metal part 4at this point even under high clamping forces. In addition, bridge 23fits into the thread of clamp screw 11 by virtue of the indicateddimensioning and at the same time forms a screw locking device.

The mechanical strength of screw clamp 2 is further increased byextensions 24, 25 which project in one piece from outer end part 12 ofarm section 5 and which, bent by roughly 90°, each penetrate with theirneck parts 26 corresponding to recess 27 of inner end part 15. Theextensions fit behind the inner edge areas of recesses 27 with singlelug 28 or double lug 29, which runs transversely to neck part 26,without projecting above screw terminal 2.

The diameter of screw head 30 has a size corresponding to the terminalwidth such that it does not increase the terminal dimensions andnevertheless can convert the total tightening torque into clampingforce.

The distance of center point M of opening 18 of inner end part 15 fromits free front edge 31 is smaller than the diameter of the circle, sothat a circular opening of roughly two-thirds of the circle diameterarises by which two sickle-shaped claws 32 are formed which encompassthe screw. This version is, moreover, much more easily managed in termsof production engineering than a opening that touches the front edge ifthe diameter of threaded shaft 19 is equal to the arm clearance.

FIG. 4 shows a connection-side front view of the connector-contactcarrier with the terminal bushings inserted. FIG. 5 shows a partiallycutaway side view of the contact carrier with terminal bushingsinserted. Four of the terminal bushings shown in FIGS. 1-3 are locatedin contact cavities 33 of contact carrier 34 of a miniature plug.Stripped ends 35 of pertinent stranded wires 36 are each insertedbetween cross nut 9 and arched bottom part 37 of U-shaped sheet metalpart 4 and are terminal-contacted by terminal screw 11, which is turnedtransversely to the direction of insertion. Screw head 30 in this caselies in a matched hole of wall 38 of contact carrier 34, the wall beingadjacent to the outside surface of end part 12 of first arm section 5.At the same time, the terminal bushing is held in contact cavity 33.

To insert contact pins of a mating connector which is not shown in theelongation of contact cavities 33 there are slots 39 that extend towardfront side 40 of contact carrier 34. To attach the contact carrier in ahousing of the miniature plug which is not shown by means of the centralscrew, contact carrier 34 has central hole 41.

Overall, by means of the described features, a screw clamp that can beused, for example, in a terminal sleeve can be formed with extremely lowcost, but which, in spite of minimum dimensions, has high stability.

I claim:
 1. A screw terminal for connecting electrical conductorscomprising:a U-shaped sheet metal part; a cross nut between a first armsection and a second arm section held using side shoulders in a recessof the first arm section and a recess of the second arm section andlocated transversely to the first arm section and the second arm sectionfor holding and guiding a threaded shaft of a terminal screw; an outerend part of the first arm section bent by 90° towards the second armsection, wherein the outer end part of the first arm section lies on thesecond arm section and has a central hole for penetration of thethreaded shaft of the terminal screw; an inner end part of the secondarm section bent 90° towards the first arm section around a bendingedge, wherein the inner end part rests flat against the outer end partand has an opening that is flush with the central hole of the outer endpart for penetration of the threaded shaft of the terminal screw.
 2. Ascrew terminal according to claim 1, wherein the outer end part of thefirst arm section between the first arm section and the second armsection bears one-piece extensions with a neck and at least one lug thatprojects laterally from the neck, and wherein the extensions, which arebent 90° when the screw terminal is installed, align with the neckcorresponding to recesses of the inner end part and fit behind inneredge parts of the recesses of the inner end part with said at least onelug.
 3. A screw terminal according to claim 1, wherein the opening ofthe inner end part in cross section is the flat segment of a circle witha chord that runs parallel to the bending edge and has a distance atleast roughly corresponding to the core radium of the threaded shaftfrom a center point of the circle.
 4. A screw terminal according toclaim 1, wherein the recess in the second arm section further comprisesa boundary edge defining a Jog between the boundary edge and the bendingedge, and wherein the boundary edge and the bending edge are separatedby a distance substantially equal to the thickness of the sheet metalpart.
 5. A screw terminal according to claim 1, wherein the opening ofthe inner end part in cross section is an unclosed circle in which thedistance of a center point from a front edge of the inner end part, thefront edge being parallel to a wall of the second arm section, is lessthan a radius corresponding to an outside diameter of the threaded shaftof the terminal screw.
 6. A screw terminal according to claim 1, furthercomprising a locking mechanism connected to the outer end part and theinner end part.
 7. A screw terminal according to claim 1, wherein theterminal screw penetrates the central hole of the outer end part, theopening of the inner end part, and the cross nut.